Method of vulcanising pneumatic tyres and apparatus therefor

ABSTRACT

A tire enclosed in a vulcanization mold is supplied with heat to cause vulcanization of same. By thermal-detection probes introduced into the tire monitoring of the cross-linking degree reached in at least one first detection region and one second detection region disposed within the tire is carried out. Head supply is stopped on occurrence of the following conditions: (i) the crosslinking degree measured in at least one of the detection regions reaches a first reference value higher than 90% of the whole cross-linking; and (ii) the cross-linking degree measured in each detection region has overcome a second pre-established reference value not exceeding about 50% of the whole cross-linking.

CROSS REFERENCE TO RELATED APPLICATION

This application is a national phase application based onPCT/IT2005/000622, filed Oct. 27, 2005, the content of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and an apparatus forvulcanising pneumatic tyres.

2. Description of the Related Art

Generally, in the manufacture of pneumatic tyres for vehicle wheels itis provided that a moulding and vulcanisation treatment be carried outsubsequently to a step of building the green tyre through assembly ofthe respective components, each of which has its own elastomercomposition, and some of which are equipped with suitable reinforcingstructures; said treatment aims at determining the structuralstabilisation of the tyre through cross-linking of said elastomercompositions and at the same time, as generally required, enablesformation of a desired tread pattern thereon as well as of possibledistinctive graphic marks at the tyre sidewalls.

To this aim, the green tyre is introduced into a suitably heatedvulcanisation mould having a moulding cavity of a shape conforming tothe final shape to be given to the tyre itself.

After closure of the mould has occurred, the green tyre is pressedagainst the holding walls of the moulding cavity while simultaneouslythe necessary heat to carry out vulcanisation of the tyre itself issupplied. For the purpose, a bladder of toroidal conformation forexample, is caused to expand within the tyre through admission of steamunder pressure into said bladder, so as to bring the latter into contactwith the inner surface of the tyre and compress said tyre against theholding walls of the moulding cavity.

The steam under pressure admitted to the expanded bladder within thetyre is also used to supply part of the necessary heat forvulcanisation. Another heat portion is supplied through the mould fromthe outside of the tyre, suitably heated by means of pipelines forcirculation of steam or other heating fluid that are arranged in thevulcanisation apparatus.

Usually, the steam-supply temperature and pressure and the residencetime of the tyre in the vulcanisation mould are managed following apre-established program, obtained based on experimental data, so as tobring the tyre components having different elastomer compositions to adesired cross-linking degree.

When vulcanisation has been completed, supply of heat is stopped and themould is opened to enable removal of the tyre and prepare the mould to anew moulding/vulcanisation cycle.

By so doing however, phenomena of over-vulcanisation and/or insufficientvulcanisation of the tyre or parts thereof can easily occur. Thesephenomena can, for example, take place following variations in thetemperature of the steam used to heat the moulds. In addition,variations in the mould temperature can also occur, due to variations inthe ambient temperature for example, or in the temperature of theheating fluids and the amount of heat dissipated by the mould in thetime unit and/or in the opening periods of same between the end of avulcanisation step and the beginning of vulcanisation on a subsequenttyre.

In an attempt to eliminate the above described problems, U.S. Pat. No.3,718,721 proposes a method of controlling the vulcanisation state of atleast one portion of a tyre during supply of heat to the same, accordingto which a probe for temperature detection is introduced into apredetermined tyre region.

During supply of heat to the tyre, detection of the temperature of theelastomer material in relation to time is carried out close to theprobe, to calculate the true vulcanisation state reached by the tyreportion where the probe is inserted. On achievement of a predeterminedcross-linking degree, supply of heat is stopped.

According to the teachings of U.S. Pat. No. 3,718,721, the probe formeasurement of the temperature to be detected is disposed in a tyreregion where heat transmission takes place with great difficulty, or inany case where the lowest cross-linking degree is expected to be reachedat the end of the process. Should the presence of several probes atdifferent tyre regions be provided, interruption of heat supply will becarried out based on the data sent by the probe detecting the lowestcross-linking degree. Bringing said tyre region to the rightcross-linking degree will guarantee a sufficient vulcanisation also ofthe remaining tyre portions.

SUMMARY OF THE INVENTION

The Applicant has however noticed that also the method disclosed in U.S.Pat. No. 3,718,721 is unable to ensure an optimal control of thevulcanisation process.

The Applicant could in fact observe that an influence on the overallvulcanisation time is produced by the great number of hardly predictableand uncontrollable factors that can, depending on temperature,significantly affect the dynamics according to which heating in thedifferent tyre regions takes place. For instance, the Applicant hasobserved that the temperature of the elastomeric components in the greentyre at the beginning of the vulcanisation step can significantly affectthe dynamics according to which heating takes place in the differenttyre regions.

Another important factor is the outdoor ambient temperature because thetemperature of the green tyre introduced into the mould can dependthereon, as well as, as a result, the temperature gradients in thedifferent tyre regions, above all in the initial steps of thevulcanisation process.

In addition, according to the Applicant's perception, the methoddisclosed in U.S. Pat. No. 3,718,721 would appear to be disadvantageousalso in terms of productivity and costs because the vulcanisation ofeach tyre would basically require much longer times than necessary.

Another hardly controllable factor, above all in the productionprocesses that do not involve storage of semifinished items during thetyre production (see document WO 01/32409 in the name of the Applicant,for example) is the time elapsing between production of each of the tyrecomponents and introduction of the green tyre into the mould. Duringthis temporary step in fact, the elastomeric components are submitted tocooling the degree of which depends on the outdoor temperature and,exactly on the above stated time gap.

The outdoor temperature can also affect heat dissipation from the mouldin the period elapsing between opening of the mould itself for removalof the finished tyre and introduction of a new green tyre.

The Applicant has sensed that the control of a vulcanisation processcarried out following the teachings of U.S. Pat. No. 3,718,721 coulddetermine production of tyres which, at some regions, have a sufficientcross-linking degree to ensure the structural integrity of the tyre forpurposes of safety in running, but are not optimal in terms ofperformance. For example, the elastomeric component may happen to have across-linking degree at the radially external portions of the tread bandor at the bead, depending on circumstances, that is higher or on thecontrary lower than the optimal cross-linking degree required for bestperformance.

This circumstance represents a problem of great importance, above all inmanufacturing tyres for cars and/or motorcycles of high and very highperformance, and/or to be used for competitions, where an excellentqualitative level also from the point of view of performance isrequired.

The Applicant has sensed that it is possible to significantly improvethe present vulcanising methods by monitoring the cross-linking degreereached at least at two regions of the tyre.

Monitoring enables the supply of heat to be stopped at the moment thatin a first tyre region a desired cross-linking degree has been reachedwhich is adapted to ensure the performance characteristics of the tyre,and in a second tyre region a cross-linking degree higher than a minimumpredetermined value capable of ensuring the characteristics ofstructural integrity of the tyre has been reached.

In particular, this first region is preferably part of the tread band,while the second region can preferably be part of the tread band too orof another tyre portion such as the bead region.

In more detail, in a first aspect, the present invention relates to amethod of vulcanising pneumatic tyres, comprising the steps of:

-   -   shutting a green tyre in a vulcanisation mould;    -   supplying heat to the tyre to cause vulcanisation of same;    -   monitoring, during heat supply, a first value of the        cross-linking degree reached in a first detection region and a        second value of the cross-linking degree reached in a second        detection region, said first and second detection regions being        disposed within the tyre;    -   stopping heat supply upon occurrence of the following        conditions:        i) the first value of the cross-linking degree reaches a first        reference value higher than about 90%;        (ii) the second value of the cross-linking degree has overcome a        second reference value which is lower than about 50%.

In a further aspect, the present invention relates to an apparatus forvulcanising pneumatic tyres, comprising:

-   -   a vulcanisation mould having a moulding cavity for at least one        green tyre;    -   devices for heat supply to the green tyre shut in the        vulcanisation mould, to determine vulcanisation of same;    -   devices for monitoring a first value of the cross-linking degree        reached in a first detection region and a second value of the        cross-linking degree reached in a second detection region, said        first and second detection regions being disposed within the        tyre;    -   control devices co-operating with the monitoring devices to stop        heat supply when the first value of the cross-linking degree        reaches a first reference value higher than about 90%, while the        second value of the cross-linking degree has overcome a second        reference value which is lower than about 50%.

Further features and advantages will be more apparent from the detaileddescription of a preferred, but not exclusive, embodiment of a methodand an apparatus for vulcanising pneumatic tyres, in accordance with thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

This description will be set out hereinafter with reference to theaccompanying drawings, given by way of non-limiting example, in which:

FIG. 1 diagrammatically shows one half in diametrical section of avulcanisation mould being part of an apparatus for manufacturing tyresfor vehicle wheels in accordance with the present invention;

FIG. 2 shows an enlarged detail of FIG. 1 highlighting positioning ofthe thermal-detection probes within the mould;

FIG. 3 is a graph obtainable from a laboratory test aiming at detectingthe cross-linking degree against time of a test piece to a predeterminedreference temperature;

FIG. 4 is a graph showing the variation in the cross-linking degree indifferent detection regions of a tyre submitted to a vulcanising processin accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, an apparatus for vulcanising pneumatic tyresof vehicle wheels in accordance with the present invention has beengenerally identified with reference numeral 1.

Apparatus 1 generally comprises a vulcanisation mould 3 defining amoulding cavity 3 a adapted to receive a green tyre 2 to be submitted toa moulding and vulcanising process.

As shown in FIG. 1, the vulcanisation mould 3 has a pair of axiallyopposite plates 4 and a plurality of circumferential sectors 5 movablein a mutually approaching direction concurrently with closure of themould 3. On closure of the mould, the plates 4 and sectors 5 define aninner surface 6 of the moulding cavity 3 a the shape of which matchesthe final conformation to be given to tyre 2. In more detail, plates 4are set to operate at the so-called beads 7 and sidewalls 8 of the tyre2 being processed, while sectors 5 are adapted to operate on a treadband 9 of the tyre itself. The green tyre 2, once shut in mould 1, ispressed against the inner surface 6 of the moulding cavity 3 a by asuitable device. Subsequently, or simultaneously with the pressing step,heat is supplied to the green tyre 2 pressed against said inner surface6.

By effect of pressing, suitable ridges arranged on the sectors 5 andplates 4 cause formation of a desired pattern on the tread band 9 oftyre 2, as well as of a plurality of distinctive graphic marks on thesidewalls 6.

The supplied heat causes cross-linking of the different elastomercompositions of which the tyre is made up. When the cycle has beencompleted, the finished tyre (i.e. the moulded and cured tyre) is drawnout of the mould 3, after opening of the latter.

Shown in FIG. 1 by way of example is a pressing device comprising abladder 10 of substantially toroidal conformation having twocircumferential edges carrying respective anchoring tailpieces 10 a tobe sealingly engaged in the mould 3. A duct 11 formed in mould 3 foradmitting steam or other operating fluid converges at the inside ofbladder 10 so as to enable expansion of the latter following admissionof fluid under pressure, thereby compressing the green tyre 2 againstthe plates 4 and sectors 5. Also operatively associated with mould 3, atplates 4 and/or sectors 5, are devices 12 to supply heat to the greentyre 2 to be vulcanised, which devices preferably co-operate with thesteam admitted to the expandable bladder 10.

The vulcanisation mould 3 preferably further comprises a plurality ofvent valves 13 mounted to regions of mould 3 close to the tyre shouldersand crown area, for example. The vent valves 13 mounted in respectivethrough seats 13 a arranged in the mould walls, perform the function of,concurrently with the pressing step, evacuating air pockets or otherfluid possibly used in the vulcanisation process and present between thegreen tyre 2 and inner surface 6.

Also operatively associated with mould 3 are devices 14, 15, 18 formonitoring the value of the cross-linking degree reached by tyre 2,which devices are operatively connected with an electronic control unit17 or other suitable control devices to stop heat supply to the tyrewhen a desired value of the cross-linking degree, to be better definedin the following, has been reached.

In more detail, the monitoring devices 14, 15, 18 comprise at least onefirst thermal-detection probe 14 and one second thermal-detection probe15 operating on a first detection region 14 a and a second detectionregion 15 a respectively, defined in the tyre being processed.

Each of the thermal-detection probes 14, 15 projects a predeterminedamount from the inner surface 6 of the moulding cavity 3 a, so that itis included in the material having a specific elastomer composition andforming tyre 2 in the respective detection region 14 a, 15 a. As betterviewed from FIG. 2, the thermal-detection probes 14, 15 preferablyproject from the inner surface 6 of the moulding cavity 3 a byrespectively different amounts, so that the first and second detectionregions 14 a, 15 a are located in tyre 2 at respectively differentdepths, i.e. one at a radially more inward position than the other.

Preferably the thermal-detection probes 14, 15, or at least one of them,are associated with one of sectors 5 so that they project in themoulding cavity 3 a close to the region set to operate against the treadband 9 of tyre 2.

By way of example, the first thermal-detection probe 14 can project fromthe moulding cavity 3 a by an amount ranging between about 0.5 and about3 mm, preferably of about 1 mm, so that the first detection region 14 ais located at the outer surface of the tread band 9, to a distance that,by way of indication, is included between about 10% and about 30% of thetread thickness, where control of the cross-linking degree isparticularly critical in relation to the performance characteristics oftyre 2 during use.

The second thermal-detection probe 15 in turn can project from the innersurface 6 of the moulding cavity 3 a by an amount that, by way ofindication, is included between about 1.5 and about 10 mm, preferably ofabout 8 mm, so that the second detection region 15 a is located to adistance included, by way of indication, between about 70% and about 90%of the tread thickness, close to a belt structure 16 or other textile ormetallic reinforcing structure usually integrated into tyre 2. To avoiddamages to the belt structure 16 and/or the second thermal-detectionprobe 15, the probe itself may be provided to project from the innersurface 6 of the moulding cavity 3 a by an amount that in any case doesnot exceed the amount of projection of the ridges 5 a usually arrangedin sectors 5 to form the above mentioned pattern on the tread band 9. Inthis manner, the second probe 15 and the respective detection region 15a keep a distance ranging, by way of indication, between about 0.5 andabout 3 mm from the belt structure 16 or other textile or metallicreinforcing structure integrated into tyre 2.

Preferably, the first and/or second thermal-detection probes 14, 15project from the inner surface 6 of the moulding cavity 3 a in parallelto the movement direction of the respective sector 5, plate 4 or othermovable portion during the opening and closing steps of mould 3.

Each probe 14, 15 therefore projects from the inner surface 6 of mould 3in a direction substantially parallel to the mutual approachingdirection between the inner surface 6 of mould 3 and the outer surfaceof tyre 2, during closure of mould 3. In this way transmission ofundesirable bending stresses to the probes 14, 15 is avoided in theopening and closing steps of mould 3. It is therefore advantageouslypossible to use particularly thin probes 14, 15 to be housed in thethrough seats 13 a in place of the vent valves 13, and having sizesadapted neither to cause changes in the geometrical and structuralfeatures of tyre 2, nor to produce clear footprints in the finishedproduct.

During heat supply to tyre 2 enclosed in mould 3, the probes 14, 15 sendthe electronic control unit 17 signals representing the temperaturereached by tyre 2 in the first and second detection regions 14 a, 15 a,respectively. Temperature detection through probes 14, 15 is carried outcyclically at relatively near time intervals, in the order of about 1second for example, and preferably in the range between 0.1 and 60seconds, so as to substantially carry out a continuous monitoring on thetemperature course during the whole vulcanisation cycle.

All data representative of temperatures are processed by the electroniccontrol unit 17 according to a suitable preset algorithm, following theArrhenius law for example, to monitor the cross-linking degree deducedfrom a corresponding equivalent time (as hereinafter defined), that isgradually reached by the elastomer compositions present in the first andsecond detection regions 14 a, 15 a.

Preferably, the cross-linking degree is determined based on thefollowing Arrhenius equation:t1/t2=exp[−E/R(1/T2−1/T1)]wherein:

-   -   R=universal gas constant;    -   E=energy of activation of the cross-linking reaction,        characteristic typical of the cross-linkable elastomer        composition used;    -   t1=time required for obtaining the desired cross-linking degree        at a constant reference temperature T1;    -   t2=Time required for obtaining the desired cross-linking degree        at a constant temperature T2.

Consequently, being known time t2 for reaching a desired cross-linkingstate at a specified constant temperature T2, it is possible tocalculate time t1 required for reaching the same cross-linking state atthe reference temperature T1. Time t1 is commonly referred to as“equivalent time” for cross-linking.

Previously entered in a storage unit associated with the electroniccontrol unit 17, in relation to the elastomer composition present in thefirst and/or second detection regions 14 a, 15 a, are datarepresentative of the required equivalent time so that the cross-linkingdegree may reach a first reference value ranging, by way of indication,between 95% and 100% and preferably higher than about 90% of the fullcross-linking. Also entered in the storage unit 17 in relation to theelastomer composition present in the first and/or second detectionregion 14 a, 15 a are data representative of the required equivalenttime so that, at said reference temperature, the cross-linking degreemay reach a second pre-established reference value smaller than thefirst reference value. The second reference value is preferably includedbetween 25% and 35%, and, just as an indication, it must not exceedabout 50% of the full cross-linking.

Said data representative of the equivalent time, stored in the controlunit 17, are previously established based on a laboratory test, carriedout following the ISO 6502 standard for example, on a test piece of theelastomer composition present in the detection region itself and notcross-linked.

FIG. 3 is a graph obtainable from a typical laboratory test in whichcurve K represents the elastic reaction F opposed by the test piece intime t. As can be seen, in a starting step A of the test the elasticreaction F suffers a slight reduction, by effect of the reducedviscosity of the material following heating, until a minimum value Fminis reached that is conventionally considered as a reference representinga cross-linking degree equal to zero. After the starting step A has beenovercome, the elastic reaction F progressively increases until a maximumvalue Fmax is reached, which is conventionally allocated a per centcross-linking degree equal to 100.

At each point P1, P2 of the curve length K subtending step B, the percent value of the cross-linking degree reached by the material in thecorresponding instant t1, t2 is expressed by:100×(F1−Fmin)/(Fmax−Fmin)100×(F2−Fmin)/(Fmax−Fmin), respectively,wherein F1 or F2 represents the elastic reaction value of the test pieceat the instant t1 or t2.

The experimental data acquired during laboratory tests carried out ontest pieces of the elastomer composition used in the detection region oftyre 2 are stored in the electronic control unit 17, so that the lattercan calculate the cross-linking degree reached in the detection regions14 a, 15 a, based on the data relating to the cyclically measuredtemperatures in time by the first and second thermal detection probes14, 15.

In particular, using the equivalent-time values calculated at eachreading cycle carried out by probes 14, 15, the electronic control unit17 is able to calculate the cross-linking degree reached at each instantby said elastomer composition in the first and second detection regions14 a, 15 a.

At each reading cycle of the thermal-detection probes 14, 15, theelectronic control unit 17 compares the cross-linking degree calculatedfor each of the detection regions 14 a, 15 a with the respective firstand second reference values, to operate interruption of heat supply,preferably concurrently with opening of mould 3, on occurrence of thefollowing conditions:

-   -   (i) the value of the measured cross-linking degree at least at        one of said detection regions 14 a, 15 a (preferably at the fist        detection region 14 a since the latter is close to the surface        of the tread band 9) reaches a first reference value higher than        about 90%;    -   (ii) the cross-linking degree measured at each of the detection        regions 14 a, 15 a has overcome a second reference value which        is lower than about 50%.

Preferably the first reference value is included between about 95 andabout 100%. Preferably the second reference value is included betweenabout 25 and about 35%.

In this manner, a guarantee exists that at a given region of tyre 2,close to the outer surface of the tread band 9 for example where thefirst detection region 14 a is measured, an optimal cross-linking degreeas to the desired performance characteristics of tyre 2 is reached.Meanwhile, the control carried out in the second detection region 15 aand/or other possible detection regions concerning inner parts of tyre 2for example, that can be reached by heat with more difficulty, ensuresthat heat supply will not be stopped before the cross-linking degree insaid parts has reached a value that, although still lower than theoptimal cross-linking degree required in the first detection region 14a, is suitable to preserve the structural integrity of tyre 2 in use.

FIG. 4 is a graph illustrating the variation in the cross-linking degreemeasured following the above statements at different detection regions14 a, 15 a of a tyre 2, in a vulcanisation cycle carried out inaccordance with the invention.

Curves S1 and S2 represent the cross-linking degree against timerespectively measured at the first detection region 14 a located closeto the outer surface of the tread band 9, and at the second detectionregion 15 a disposed at a more inward position, close to the beltstructure 16.

It is possible to observe that near the first detection region 14 a,placed in close proximity to the inner surface 6 of the moulding cavity3 a and therefore very close to the heat supply source, thecross-linking degree (curve S1) increases more quickly than in thesecond detection region 15 a. Consequently, the cross-linking degree inthe first detection region 14 a overcomes the second reference value V2at instant t1, when the cross-linking degree in the second detectionregion 15 a (curve S2) is still under the second value. As thevulcanisation cycle advances, the cross-linking degree overcomes thesecond reference value V2 in the second detection region 15 a too atinstant t2, when the cross-linking degree in the first detection region14 a is still under the first reference value V1. Consequently, heatsupply goes on, until instant t4 at which the cross-linking degree inthe first detection region 14 a reaches the first reference value V1. Assoon as this value is overcome, the electronic control unit 17 operatesinterruption of heat supply and opening of mould 3, to allow removal oftyre 2.

The cross-linking process in tyre 2 can go on over a certain period oftime after extraction of the tyre itself from mould 3, by effect of theheat stored in tyre 2.

Positioning of the first and second thermal-detection probes 14 and 15can be different from the previously described one, depending on thetype and/or destination of use of tyre 2 being processed. The previouslydescribed example is particularly suitable, by way of indication, forhigh-performance tyres for sports uses, where the grip offered by thetread band 9 takes a particularly important role as regards thequalitative evaluation of tyre 2.

In other situations, a control of the cross-linking degree at the beads7 of tyre 2 can be wished. In this case the first and/or secondthermal-detection probes 14 and/or 15 can be placed in such a manner asto project in the moulding cavity 3 a at a radially inner region set tooperate against the tyre bead 7 where the first and/or secondthermal-detection regions 14 a, 15 a will be defined.

As exemplified in the accompanying drawings, the cross-linking degreeclose to the bead 7 or any other desired third detection region 18 a oftyre 2 can also be monitored by means of at least one thirdthermal-detection probe 18 interlocked with the electronic control unit17. The electronic control unit 17 inhibits interruption of heat supplywhen the cross-linking degree measured by the third probe 18 is lowerthan a third reference value V3 which is lower than the first referencevalue V1. The third reference value V3 can equal or be different fromthe second reference value V2; in the example shown in FIG. 4 V3 ishigher than V2.

In said FIG. 4, curve S2 relating to the third thermal-detection probe18 is drawn; it reaches the third reference value V3 at an instant t3subsequent to overcoming of the second reference value V2 in the seconddetection region 15 a. However, on reaching of the third reference valueV3 in the third detection region 18 a, the cross-linking degree in thefirst detection region 14 a has not yet reached the first referencevalue V1. Consequently, heat supply goes on until the first referencevalue V1 is reached in the first detection region 14 a.

In accordance with a further preferential aspect of the presentinvention, the presence of probes 14, 15, 18 can be advantageously alsoexploited for monitoring the heat-distribution homogeneity within thetyre 2 being processed. To this aim, associated with the electroniccontrol unit 17 can be at least one comparator 19 operativelyinterconnected with the thermal-detection probes 14, 15, 18 to comparedata relating to the temperatures measured by each probe with eachother, simultaneously with each of the detection cycles carried out byit. Comparator 19 calculates the difference between the temperaturesmeasured by probes 14, 15, 18 at each detection cycle and compares theobtained result with the threshold value previously inputted to astorage unit. An excessive difference between the temperatures measuredby the individual probes 14, 15, 18 is an indication of a probablemalfunction of one or more of said probes. Advantageously, when thedifference between the temperatures measured by the individual probes14, 15, 18 overcomes the previously inputted threshold value, theelectronic control unit 17 can disable control of the vulcanisationprocess, based on the data measured by the probes 14, 15, 18, in orderto enable heat supply, based on a first previously entered alternativeprogram ensuring heat supply for a period of time adapted to guaranteethat a sufficient cross-linking degree will be reached in the wholestructure of tyre 2. Since this first alternative program is to bemanaged in the absence of the data measured by the probes 14, 15, 18, itwill necessarily involve vulcanisation times different from thoseobtainable by carrying out the control through said probes 14, 15, 18,but at all events it will enable the vulcanisation process to be carriedout.

Also provided can be use of at least one auxiliary thermal-detectionprobe 20 operatively disposed in the mould 3 to detect the temperaturewithin the mould itself. Preferably, the auxiliary probe 20 operates ata distance ranging between about 2 mm and about 35 mm from the innersurface 6 of the moulding cavity 3 a. Preferably said distance isincluded between about 2 mm and about 10 mm.

The auxiliary probe 20 is operatively connected to comparator 19interlocked with said first, second and/or third detection probes 14,15, 18, or other distinct comparator carrying out a comparison betweenthe temperature measured by the auxiliary probe 20 and a preset limitvalue, stored on the memory. During the heating step of thevulcanisation apparatus 1, the auxiliary detection probe 20 can beexploited to guarantee that mould 3 has reached an optimal operativetemperature before starting the vulcanisation process. To this aim, theelectronic control unit 17 is adapted to enable introduction of tyre 2into mould 3 and/or closure of said mould 3, when the difference betweenthe temperature measured by the auxiliary probe 20 and the preset limitvalue is lower than a predetermined acceptability threshold. Duringaccomplishment of the vulcanisation process, an excessive deviation ofthe temperature of mould 3 from the optimal operative temperature is anindication of a probable malfunction of the thermal-detection probes 14,15, 18 operating in tyre 2. Therefore, the electronic control unit 17can advantageously interact with comparator 19 to enable heat supplybased on a second pre-established alternative program, when the percentdifference between the temperature of the vulcanisation mould 3 and thetemperature measured by the probes 14, 15, 18 operating within tyre 2overcomes a pre-established value, included, by way of indication,between about 3% and about 10%. Based on the second alternative program,adjustment of the vulcanisation time, i.e. interruption of heat supplywhen vulcanisation has been completed, can be controlled based on thetemperature measured by the auxiliary probe 20 directly operating withinthe mould 3. In this case too, the vulcanisation time will be regulatedin such a manner as to ensure a sufficient cross-linking degree withintyre 2, and basically will be different from that obtainable by thecontrol carried out by the first, second and/or third thermal-detectionprobes operating in tyre 2.

1. A method of vulcanising pneumatic tyres, comprising the steps of:shutting a green tyre in a vulcanisation mould; supplying heat to thetyre to cause vulcanisation of same; monitoring, during heat supply, afirst value of cross-linking degree reached in a first detection regionand a second value of cross-linking degree reached in a second detectionregion, said first and second detection regions being disposed withinthe tyre; and stopping heat supply upon occurrence of the followingconditions: the first value of the cross-linking degree reaches a firstreference value higher than about 90%; and the second value of thecross-linking degree has overcome a second reference value which islower than about 50%.
 2. The method as claimed in claim 1, wherein themonitoring step is carried out by cyclically calculating the value ofthe cross-linking degree reached in said detection regions atpredetermined time intervals.
 3. The method as claimed in claim 1,wherein monitoring of the value of the cross-linking degree in each ofsaid detection regions comprises the steps of: cyclically measuring thetemperature in each detection region at predetermined time intervals;and calculating the value of the cross-linking degree reached in eachdetection region based on measured temperature values.
 4. The method asclaimed in claim 2, wherein cyclical calculation of the value of thecross-linking degree is carried out at time intervals between about 0.1and about 60 seconds.
 5. The method as claimed in claim 1, wherein oneof at least the first and second detection regions is at a radially moreinward position than the other.
 6. The method as claimed in claim 1,wherein at least one of said detection regions is substantially at adistance between about 0.5 and about 3 mm from an outer surface of thetyre.
 7. The method as claimed in claim 1, wherein at least one of saiddetection regions is substantially at a distance between about 1.5 andabout 10 mm from an outer surface of the tyre.
 8. The method as claimedin claim 1, wherein at least one of said detection regions is disposedat a distance between about 0.5 and about 3 mm from a textile ormetallic reinforcing structure integrated into the tyre.
 9. The methodas claimed in claim 1, wherein at least one of said detection regions isdisposed close to a tread band of the tyre.
 10. The method as claimed inclaim 9, wherein said detection region at the tread band is disposed ata radially internal position relative to a radially external position ofthe tread band at a distance between about 10% and about 30% of thetread thickness.
 11. The method as claimed in claim 9, wherein saiddetection region at the tread band is disposed at a radially internalposition relative to a radially external surface of the tread band at adistance between about 70% and about 90% of the tread thickness.
 12. Themethod as claimed in claim 1, wherein at least one of said detectionregions is substantially disposed close to a bead of the tyre.
 13. Themethod as claimed in claim 1, further comprising the step of monitoringthe value of the cross-linking degree in at least one third detectionregion in the tyre during heat supply.
 14. The method as claimed inclaim 13, wherein interruption of heat supply is inhibited when thevalue of the cross-linking degree measured at the third detection regionis lower than a third reference value which is lower than said firstreference value.
 15. The method as claimed in claim 3, furthercomprising the steps of: comparing with each other, the temperaturesrespectively measured in said detection regions; and enabling heatsupply based on a first alternative program, when the difference betweenthe temperatures respectively measured overcomes a predeterminedthreshold.
 16. The method as claimed in claim 3, further comprising thesteps of: measuring vulcanisation mould temperature before shutting thetyre in the mould; comparing temperature measured in the mould with apreviously entered limit value; and enabling shutting of the tyre in themould when the difference between the temperature measured in the mouldand a previously entered limit value is lower than a predeterminedacceptability threshold.
 17. The method as claimed in claim 3, furthercomprising the steps of: measuring vulcanisation mould temperature;comparing the vulcanisation mould temperature with the temperaturemeasured in at least one of said detection regions; and enabling heatsupply based on a second alternative program, when the differencebetween the vulcanisation mould temperature and the temperature measuredin at least one of said detection regions overcomes a predeterminedvalue.
 18. The method as claimed in claim 16, wherein the mouldtemperature is measured at a distance between about 2 mm and about 10 mmfrom an inner surface of the mould set to act against the tyre.
 19. Themethod as claimed in claim 3, wherein temperature measurement in atleast one of said detection regions is carried out by a probe projectingfrom an inner surface of the mould in a direction substantially parallelto a mutual-approaching direction between the inner surface of the mouldand an outer surface of the tyre during shutting of the tyre in themould.
 20. The method as claimed in claim 1, wherein the first referencevalue is between 95% and 100%.
 21. The method as claimed in claim 1wherein the second reference value is between 25% and 35%.
 22. Anapparatus for vulcanising pneumatic tyres, comprising: a vulcanisingmould having a moulding cavity for at least one green tyre; devices forheat supply to the green tyre shut in the vulcanisation mould to causevulcanisation of same; monitoring devices for monitoring a first valueof cross-linking degree reached in a first detection region and a secondvalue of cross-linking degree reached in a second detection region, saidfirst and second detection regions being disposed within the tyre; andcontrol devices co-operating with the monitoring devices to stop heatsupply when the first value of the cross-linking degree reaches a firstreference value higher than about 90%, while the second value of thecross-linking degree has overcome a second reference value which islower than about 50%.
 23. The apparatus as claimed in claim 22, whereineach of said monitoring devices cyclically, at predetermined timeintervals, calculates the cross-linking degree reached in said detectionregions.
 24. The apparatus as claimed in claim 22, wherein saidmonitoring devices comprise: at least one first thermal-detection probe;at least one second thermal-detection probe; and an electronic controlunit operatively connected to said first and second thermal-detectionprobes to detect the temperature in each detection region cyclically atpredetermined time intervals and to calculate the cross-linking degreereached in each detection region based on measured temperature values.25. The apparatus as claimed in claim 24, wherein each of saidthermal-detection probes projects from an inner surface of the mouldingcavity.
 26. The apparatus as claimed in claim 25, wherein thethermal-detection probes project by different amounts respectfully fromthe inner surface of the moulding cavity.
 27. The apparatus as claimedin claim 25, wherein at least one of said thermal-detection probesprojects in the moulding cavity by an amount between about 0.5 mm andabout 3 mm.
 28. The apparatus as claimed in claim 25, wherein at leastone of said thermal-detection probes projects in the moulding cavity byan amount between about 1.5 and about 10 mm.
 29. The apparatus asclaimed in claim 25, wherein at least one of said first and secondthermal-detection probes projects in the moulding cavity at a region setto operate against one tread band of the tyre.
 30. The apparatus asclaimed in claim 25, wherein at least one of said thermal-detectionprobes projects in the moulding cavity close to a radially inner regionset to operate against a bead of the tyre.
 31. The apparatus as claimedin claim 24, wherein said monitoring devices comprise at least one thirdthermal-detection probe to monitor the cross-linking degree reached inat least one third detection region.
 32. The apparatus as claimed inclaim 31, wherein said control devices inhibit interruption of heatsupply when a value of the cross-linking degree measured in the thirddetection region is lower than a third reference value which is lowerthan said first reference value.
 33. The apparatus as claimed in claim24, further comprising at least one comparator to compare with eachother, temperatures respectively measured by said thermal detectionprobes, wherein said control devices are operatively interconnected withsaid comparator to enable heat supply based on a first alternativeprogram, when the difference between temperatures respectively measuredovercomes a predetermined threshold.
 34. The apparatus as claimed inclaim 24, further comprising: at least one auxiliary thermal-detectionprobe operatively disposed in the mould to detect the vulcanisationmould temperature; a comparator to compare the temperature measured inthe mould with a previously entered limit value; wherein said controldevices are operatively interconnected with said comparator to enableshutting of the tyre in the mould when the difference between measuredtemperature in the mould and the previously entered limit value is lowerthan a predetermined acceptability threshold.
 35. The apparatus asclaimed in claim 24, further comprising: at least one auxiliarythermal-detection probe operatively disposed in the mould to detectvulcanisation mould temperature; a comparator to compare thevulcanisation mould temperature with the temperature measured by atleast one of said thermal-detection probes, wherein said control devicesare operatively interconnected with said comparator to enable heatsupply based on a second alternative program, when the differencebetween the vulcanisation mould temperature and the temperature measuredby at least one of said thermal-detection probes overcomes apredetermined value.
 36. The apparatus as claimed in claim 34, whereinthe auxiliary thermal-detection probe operates at a distance rangingfrom about 2 mm to about 10 mm from an inner surface of said mouldingcavity.
 37. The apparatus as claimed in claim 24, wherein: the mouldcomprises a plurality of portions movable in a mutually approachingdirection to shut the tyre in the moulding cavity; each of saidthermal-detection probes is carried by one of said movable portions; andat least one of said thermal-detection probes projects from an innersurface of the moulding cavity in a direction of movement of therespective movable portion during closure of the mould.